Method for the dimension checking of the timing system of an engine

ABSTRACT

A method and an associated apparatus for the dimension checking of the timing system of an internal combustion engine, in particular for checking the clearance existing between the cams of the camshaft and the relevant valves in the cylinder head, by dimensional measurements of the cylinder head and the camshaft separately, and processing, in a storing, processing and display unit, the dimensional measurements for evaluating how the camshaft actually positions itself with respect to the cylinder head on which it is mounted, in the course of the normal running of the engine.

TECHNICAL FIELD

The invention relates to a method for the dimension checking of thetiming system of an internal combustion engine comprising at least acamshaft with cams and main journals, and a cylinder head with valvesand seats for housing the main journals and defining the position of thementioned camshaft in a longitudinal direction, the method including thesteps of detecting and processing values relating to diametraldimensions of the main journals of the camshaft and radial dimensions ofthe cams, detecting and processing values relating to diametraldimensions of the seats of the cylinder head, and the transversalarrangement of the valves with respect to the formerly mentionedlongitudinal direction, and calculating--on the basis of the detectedvalues and in the course of the camshaft rotation--a clearance valuebetween each cam and its associated valve. The invention also relates toan apparatus for checking the timing system of an internal combustionengine according to the formerly mentioned method.

BACKGROUND ART

There are known internal combustion engines with mechanical tappetcomprising elements commonly called "bucket type tappets" positionedbetween the cylinder head valves and the associated cams of the camshaftand having the purpose of remaining in contact with the valves andcooperating with the cams lobes in the course of the camshaft rotation.In order to ensure a correct performance in the valve opening andclosure phases, it is necessary that the clearance existing between thebase circle of each cam and the related bucket type tappet be determinedin an accurate way.

In fact, if on the one hand no clearance, or an extremely limited amountof clearance, would not allow the proper closure of the valves, on theother hand an excessive clearance would detrimentally affect theperformance and the life of the engine and, among other things, increasenoise.

In order to attain, for each single cam/bucket type tappet coupling therequired amount of clearance, generally there is foreseen theinsertion--in a suitable bucket type tappet recess, at the cam or valveside--of a specifically thick adjustment shim so that the clearancebetween the base circle of the cam and the bucket type tappet (or theshim) be of the desired value. According to a variant, that does notinvolve the insertion of shims, there can be foreseen, for eachcam/valve coupling, the selection of an appropriate bucket type tappetamong a series of bucket type tappets that have different predeterminedthicknesses. The English abstract of Japanese patent applicationJP-A-57013205 shows a device for calculating the gaps existing betweenthe top faces of the valve lifters 3 and the base circles of therelevant cams of a camshaft when the latter is assembled to the cylinderhead. The thickness of the shims to be inserted are chosen on the basisof the values of the calculated gaps and of the desired clearances. Twomeasurements are taken to calculate each gap. A first measurement istaken on the cylinder head, substantially corresponding to the distancebetween the top surface of each bucket type valve lifter and a camshaftbearing surface 9 of the cylinder head. A second measurement is taken onthe camshaft, corresponding to the distance between the surfaces of thebase circle of the cam and a bearing journal of the camshaft.

The calculations for determining the thickness of the adjustment shims,or that of the bucket type tappets, are troublesome due to variousreasons among which the radial clearance existing between the mainjournals of the camshaft and the cylindrical seats of the cylinder headin which these journals are seated. This clearance is limited, butnecessary for guaranteeing a correct rotation of the camshaft andallowing an appropriate lubrication. Devices like the one shown in theEnglish abstract of JP-A-57013205 do not take into account such radialclearance in the calculation of the gaps.

A checking method presently used for determining the thicknessesforesees the use of apparatuses that check the dimensions of thecylinder head and those of the camshaft separately (as shown in theabove cited English abstract) and the processing of the results thusobtained by supposing that, in the course of the running of the engineand the rotating of the camshaft, the main journals of the latter--urgedby the thrust of the valve springs alternatively compressed by thevarious cams--are in constant contact with the associated cylindricalseats, at diametrally opposite positions with respect to the valves.This assumption is an approximation that depends, among other things, onthe number and the angular position of the cams on the camshaft and doesnot guarantee highly reliable results.

In order to improve the method reliability, the results can becompensated in an empiric way, on the basis of statistics on errorsdetected in the course of subsequent checkings, for example when theselected shims (or the bucket type tappets) have been inserted and thecamshaft is mounted in the cylinder head. In any case, this is not areally practical method of operating, since there is the need to collectan enormous amount of data and process them in an appropriate way, henceinvolves a considerable amount of time, high costs and not alwaysachieves satisfying results.

DISCLOSURE OF THE INVENTION

Object of the present invention is to provide a method for determiningthe thickness of plates, or shims, to be inserted in the bucket typetappets, or the thickness of the bucket type tappets, that isparticularly accurate and reliable and enables to overcome thedisadvantages of the known methods.

A further object is to provide a checking apparatus that enables toimplement this method in a simple and effective way. These objects areachieved by a method and a checking apparatus according to the presentinvention.

A method and a checking apparatus according to the invention provide themain result of determining, in an extremely accurate and reliable way,the thickness of the individual shims, or of the bucket type tappets,coupled to the valves, consequently attaining an extremely high accuracyin implementing the desired clearance between the base circle of eachcam and the associated valve.

A further advantage, that the method according to the present inventionprovides, is the application flexibility, in other terms the possibilityof attaining particularly reliable results, no matter what the shape ofthe camshaft and that of the associated cylinder head--that undergo thechecking--be.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail with reference to theenclosed sheets of drawings, given by way of non limiting example,wherein:

FIG. 1 schematically shows a first checking station for checking thecylinder head of an internal combustion engine,

FIG. 2 schematically illustrates a second checking station for dimensionchecking on a camshaft,

FIG. 3 schematically shows the arrangement of the camshaft in thecylinder head, and emphasizes the camshaft deformation by way of abroken line, with segments representing the portions comprised betweenthe cross-section centers of the main journals at the centralcross-sections (the deformation undergone by the camshaft and theclearances between journals and seats have been intentionallyexaggerated with respect to the actual conditions with the aim ofproviding clearness), and

FIG. 4 is a block diagram showing a checking method according to theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The figures numbered 1, 2 and 3 illustrate checking stations that arepart of an apparatus for implementing the method according to theinvention. More particularly, FIGS. 1, 2 and 3 show--in an extremelyschematic and incomplete way--devices for the dimension checking ofelements of the timing system of an engine while leaving out of account,for the sake of simplicity, some known structural details of thechecking systems.

The embodiment referred to in FIGS. 1, 2 and 3 regards elements of thetiming system of an internal combustion engine with four cylinders andfour valves per cylinder and two substantially identical camshafts 25(only one has been schematically illustrated in the drawings) comprisingeight cams 26, 27, 28, 29, 30, 31, 32 and 33 and four cylindricalportions or main journals 34, 35, 36 and 37. The cams 26-33 areangularly arranged by pairs in four directions spaced at 90° apart, anda main journal is placed between each pair of cams.

In FIG. 1, that refers to a first station 1 for checking a cylinder head2 of an internal combustion engine, there are shown just somefundamental elements of the cylinder head 2, more specifically, acentral body with valves 3, 3^(I), 3^(II), 3^(III), 3^(IV), 3^(V),3^(VI), 3^(VII) housed in associated openings 4 and caps 5 coupled tothe main body in a dismantable way, by means of screws (not shown in thefigure). The internal surfaces of the caps 5 define, with correspondingsurfaces of the central body of the cylinder head 2, substantiallycylindrical seats 6, 6^(I), 6^(II), 6^(III) for housing the mainjournals 34-37 of the camshaft 25 and supporting and referring theposition of the camshaft 25 in the cylinder head 2 in a longitudinaldirection. An end of each of the valves 3-3^(VII) --that can displace inreciprocally parallel transversal directions--contacts a bucket typetappet 9, 9^(I), 9^(II), 9^(III), 9^(IV), 9^(V), 9^(VI), 9^(VII) thathas a recess 10, 10^(I), 10^(II), 10^(III), 10^(IV), 10^(V), 10^(VI),10^(VII) for housing an appropriately thick adjustment shim. FIG. 1depicts, as an example only, just two adjustment shims 11 and 11^(I).Obviously, as will become apparent from the following description, inthe course of the checking operation referred to in FIG. 1, shims 11 and11^(I) are not inserted in recesses 10 and 10^(I). Compression springs12 are housed in openings 4 and urge valves 3-3^(VII) towards theexterior of the cylinder head body 2. The first checking station 1comprises a structure 13 for supporting and referring cylinder head 2and first detecting means with first gauging heads 14. Each of thegauging heads 14--of a known type--comprises a casing, coupled tostructure 13, and a pair of arms movable with respect to the casing,including associated feelers 15 for contacting diametrically oppositepoints of the seats 6, 6^(I), 6^(II) and 6^(III) at associatedtransversal, measurement cross-sections. Moreover, the gauging heads 14comprise known transducer means (not shown in the figures) connected tothe movable arms and the casing for sending to a storing, processing anddisplay unit 16 signals responsive to the deviations from the nominalvalues of the distances of the lower and upper generating lines 17 and44 of the seats 6, 6^(I), 6^(II), 6^(III), in other terms, thearrangement of these generating lines 17 and 44 with respect to thereference structure 13. Moreover, the first detecting means comprisesecond gauging heads 18 of known type too, including casings coupled tothe structure 13, and movable arms with feelers 19 for cooperating withthe bottom surfaces of the recesses 10-10^(VII) of the bucket typetappets 9-9^(VII) (FIG. 1 does not show the feelers 19 arranged in thetwo recesses 10 and 10^(I), but instead--as an example and ashereinbefore previously described--the adjustment shims 11 and 11^(I)).In gauging heads 18 there are transducer means (of a known type and notillustrated in the figures) for detecting displacements of the movablearm and providing the storing, processing and display unit 16 withsignals responsive to deviations from the nominal values of thearrangement of those surfaces, in other terms the associated transversalpositions with respect to the reference structure 13.

FIG. 2 shows a second checking station 20 comprising a second supportand reference structure 21, with elements for supporting camshaft 25,comprising a live center 22 and a dead center 23, that define alongitudinal geometrical axis.

A motor 24 is coupled to live center 22 and drives the rotation ofcamshaft 25 about the formerly mentioned longitudinal geometrical axis.

Second detecting means comprise third gauging heads 38, of a known type,with casings fixed to the support structure 21 and arms--movable withrespect to the casing--including feelers 39 for cooperating with thesurface of the main journals 34-37 at diametrically, reciprocallyopposite points at transversal cross-sections of measurement. There aretransducers (not illustrated in the drawings) connected with the movablearms for sending to the storing, processing and display unit 16 signalsresponsive to the deviations from the nominal values of the distances ofthe lower and upper generating lines 40 and 41 of the main journals34-37, in other terms, the associated transversal positions with respectto the support structure 21. The second detecting means also comprisefourth gauging heads 42, of a known type too, with casings fixed to thesupport structure 21 and movable arms with feeler elements 43 forcooperating with the surface of the cams 26-33. The transducers (notshown in the drawings) are connected with the movable arms for sendingto the storing, processing and display unit 16 signals responsive to thedeviations from the nominal values of the radial dimensions of the basecircles of the cams 26-33.

In the diagram shown in FIG. 4, the logic blocks identify the differentphases of a checking method according to the invention and hereinafterdescribed, and more specifically:

block 45: positioning of the cylinder head 2 in the first checkingstation 1;

block 46: checking the dimensions of the cylinder head 2;

block 47: processing the detected dimensions relating to cylinder head2, defining a first reference axis and calculating the dimension valueswith respect to such axis;

block 48: positioning of the camshaft 25 in the second checking station20;

block 49: positioning of the camshaft 25 in a predetermined angularposition;

block 50: detecting the dimensions of the main journals 34-37 and theradial dimensions of the cams 26-33;

block 51: processing the detected dimensions correlated with camshaft25, defining a second reference axis and calculating the dimensionvalues with respect to such axis;

block 52: checking the angular positions in which camshaft 25 hasundergone measurements in the second station 20, and comparison with apre-set number of predetermined angular positions (more specifically,four);

block 53: selecting for camshaft 25 an angular position in cylinder head2 among a certain number of predetermined positions (specifically,four);

block 54: calculating the possibility of displacement of each journal34-37 in its associated seat 6-6^(III) ;

block 55: attributing initial deviation values to the seat/journalpairs;

block 56: calculating the elastic energy stored by camshaft 25 atpredetermined deviation values;

block 57: checking relating to the calculated elastic energy;

block 58: modifying the deviation values correlated to the seat/journalpairs;

block 59: calculating the gap between a pair of cams in phase and theirassociated valves, and determining the thicknesses of the associatedadjustment shims;

block 60: verifying the number of checkings that have been performed;

block 61: ending of the procedure.

According to the invented method, the first steps to be performed areparallel checkings on cylinder head 2 and camshaft 25 at checkingstations 1 and 20, respectively, as hereinafter described. Generally,before these checkings take place, there is a calibrating phase in whichidentical checkings are performed on master pieces (with nominalreference dimensions) mounted in the two checking stations 1 and 20.

At the first checking station 1 (block 45), the cylinder head 2 ispositioned and referred on structure 13 and feelers 15 and 19 contactpairs of points on the internal surfaces of seats 6-6^(III) and thebottom surfaces of the recesses 10-10^(VII) of the bucket type tappets9-9^(VII), respectively. The first and the second gauging heads 14 and18 send to unit 16 signals responsive to the arrangement of the lowerand upper generating lines 17 and 44 of seats 6-6^(III) and,respectively, of the bottom surfaces of the recesses 10-10^(III) (block46). These latter signals are indicative of the transversal arrangementof the associated valves 3-3^(VII).

The signals representative of the arrangement of the lower and uppergenerating lines 17 and 44 of the two end seats 6, 6^(III) are processedby the storing, processing and display unit 16 for defining the positionof the cross-section centers of the end seats 6 and 6^(III), in otherterms, the position of the axes of these seats, at the transversalcross-sections of measurement, and determining a first longitudinal,reference axis passing through those centers (block 47). Hence, furtherprocessings are carried out for referring the detected dimensions to thepreviously mentioned first reference axis, and obtaining the distancevalues of the lower and upper generating lines 17 and 44 of all theseats 6-6^(III) from the first longitudinal, reference axis, and thedistances of the bottom surfaces of the recesses 10-10^(VII) of thebucket type tappets 9-9^(VII) from the first longitudinal, referenceaxis (block 47).

In the second checking station 20, camshaft 25 is positioned between thelive center 22 and the dead center 23 (block 48) and rotated by motor 24about its longitudinal geometrical axis until there is reached anangular position whereby a pair of cams 32 and 33, in phase, have theireccentric portion, or lobe, in a position that is diametrically oppositeto the feelers 43 of an associated pair of fourth gauging heads 42(block 49). This pair of gauging heads 42, with its feelers 43 thuscontacting the surface of the base circles of the cams 32 and 33, sendsto the storing, processing and display unit 16 signals responsive to theradial dimensions of the base circles.

At this angular position, the feelers 39 of the third gauging heads 38contact the main journals 34-37 and the gauging heads 38 send to unit 16associated signals responsive to the arrangement of the lower and uppergenerating lines 40 and 41 of these journals (block 50). The processingsof these signals by unit 16 comprise the checking of the position of thecross-section centers of the end journals 34 and 37, in other terms theposition of the axes of these journals at the associated cross-sectionsof measurement, and the definition of a second longitudinal, referenceaxis, passing through the formerly mentioned cross-section centers(block 51). Further simple processings enable to refer to the previouslymentioned second longitudinal axis the arrangement of both the lower andupper generating lines 40 and 41 of all journals 34-37 and thearrangements of the base circles of the pair of cams 32 and 33 (block51).

The steps described with reference to blocks 49, 50 and 51 are repeatedagain (block 52) at other three different angular positions of camshaft25, each time by rotating camshaft 25 until there is reached an angularposition at which a different pair of cams in phase 26, 27, 28, 29 and30, 31 have their lobes in positions diametrally opposite to the feelers43 of the associated fourth gauging heads 42 (block 49). At eachposition, there is defined a second longitudinal, reference axis and thearrangements (detected each time--block 50) of the generating lines ofthe main journals 34-37 and of the base circles of one of the pairs ofcams in phase 26, 27, 28, 29 and 30, 31, respectively, are referred tothis second axis (block 51). The four sequences of values processed atthe different angular positions are memorized each time in unit 16(block 51).

At each of the four angular positions taken by camshaft 25 (block 53),the values relating to the dimensions of seats 6-6^(III) of the cylinderhead 2 and the journals 34-37 of camshaft 25, that are referred to thefirst and second reference axis (blocks 47 and 51), respectively, areprocessed in unit 16 as hereinafter described, simulating an assembly ofthe camshaft 25 in the cylinder head 2 wherein these axes overlap so asto form a common single reference axis, and evaluating the possiblereciprocal positions among journals 34-37 and seats 6-6^(III).

At each seat/main journal pair (for example, pair 6/34), there aredefined, respectively, an upper maximum deviation Y³⁴ _(Smax) and alower maximum deviation Y³⁴ _(Imax) between the cross-section centers ofjournal 34 and its associated seat 6, by calculating the differencebetween the distances of the upper and lower generating lines 41, 44 and40, 17, respectively (block 54).

The maximum deviation values Y^(j) _(Smax) and Y^(j) _(Imax) (j=34, . .. , 37) thus defined for each seat/main journal pair (6/34)--and at aspecific angular position taken by camshaft 25 with respect to cylinderhead 2--delimit a range wherein there is comprised a deviation valueY^(j) (j=34, . . . , 37) among the cross-section centers of journal (34)and those of seat (6) of that pair, that represents the actualtransversal position of journal (34) in seat (6); in other terms, theposition in a transversal direction parallel to the direction ofdisplacement of valves 3-3^(III).

In order to calculate the formerly mentioned deviation Y^(j) of journals34-37 (blocks 55-59), for each of the four predetermined angularpositions taken by camshaft 25 in the cylinder head 2, it is assumedthat owing to the thrust of some of the springs 12 associated withvalves 3-3^(VII), the upper generating line 41 of one of the journals34-37 contacts the upper generating line 44 of the corresponding seat6-6^(III). Consequently, the deviation value Y^(j) of that journalcoincides with that of the associated upper maximum deviation Y^(j)_(Smax).

More specifically, assuming that camshaft 25 is mounted in the cylinderhead 2 angularly positioned, as shown in FIG. 2, the lobes of the cams32, 33 of one of the four pairs are angularly positioned in such a wayso as to contact the bucket type tappets 9^(VI) -9^(VII) of theassociated valves 3^(VI) -3^(VII) and apply a thrust for opening thesevalves. Under this condition, springs 12--associated with valves 3^(VI)-3^(VII) --apply a force to cams 32, 33 and to the journal 37 positionedtherebetween, that tends to oppose to the opening of the valves 3^(VI)-3^(VII) and is sufficient for urging journal 37 to contact theassociated seat 6^(III) at the associated upper generating lines 41 and44. Hence, it will be Y³⁷ =Y³⁷ _(Smax).

The processing in unit 16 for calculating the deviations Y^(j) (block55) includes the attributing to the deviations that refer to the otherseat/journal pairs of initial values comprised within the associatedranges delimited as already described (block 54), in particular, withreference to the previous example, (block 54) to deviations Y³⁴, Y³⁵,and Y¹⁶. For each value attributed to the Y^(j) deviations, therecorresponds a position taken by camshaft 25 in cylinder head 2, asschematically shown in FIG. 3 by way of a broken line 70, with segmentsrepresenting the portions comprised between the cross-section centers ofthe main journals 34-37. In substance, the deformations that camshaft 25undergoes when it is mounted in the cylinder head 2 and takes differentangular positions are concentrated--as schematically indicated by brokenline 70--in the areas for supporting camshaft 25 in the cylinder head 2,in other terms the seats/journals pairs.

In order to calculate the values of the deviations Y^(j) that bestapproximate the arrangement of camshaft 25 when mounted in cylinder head2, it is assumed that camshaft 25 tends to position itself in such a wayas to minimize the total amount of deformations that it undergoes, i.e.the condition in which the stored elastic energy has a minimum value.

The processings performed in unit 16 consist in evaluating (block 56)the elastic deformation energy of camshaft 25 at certain values Y^(j),and modifying the values Y^(j) (block 58) until there is reached acombination that corresponds to a total minimum value of this elasticenergy (block 57). This condition of minimum elastic energy represents aunique balance configuration for camshaft 25.

The calculating of the elastic deformation energy of camshaft 25 and thedetermining of the combination of Y^(j) values that make it minimum isachieved in a known way, hereinafter only cursorily described.

With reference to a cartesian axis x, parallel to the first longitudinalreference axis, the elastic deformation energy of camshaft 25 can beexpressed according to the following mathematical formula:

    E=k∫(d.sup.2 Y/dx.sup.2).sup.2 dx                     (1)

Where:

the integral is extended to all the length I of camshaft 25

the proportionality constant k depends on the shape of camshaft 25 andon the elasticity modulus of the material used for its manufacture and

d² Y/dx² is the curvature of the line representing the elasticdeformation of camshaft 25.

As a possible simplification, the trend of the elastic deformation line,along which the neutral axis of the camshaft 25 positions itself, can beapproximated by the broken line 70 obtained by considering thedeformations of the camshaft 25 concentrated at points corresponding tothe main journals 34-37 and, in particular, to the intermediate journals35 and 36 where the curvature assumes more significant values. Moreover,it is possible to express the curvature at each intermediate journal 35,36 with respect to the adjacent journals, as a function of thedeviations Y^(j) of the journal taken into consideration and thedeviations Y^(j-1) and Y^(j+1) of the adjacent journals, like [Y^(j)-Y^(j-1) +Y^(j+1))/2].

On the basis of such approximations, a simplified mathematicalexpression representing the elastic energy is as follows:

    E≅kΣ.sup.j [Y.sup.j (Y.sup.j -(Y.sup.j+1)/2].sup.2(2)

where j is only referred to the intermediate journals. Thus, the elasticenergy stored by camshaft 25 mounted in cylinder head 2 can beformulated as:

    E≅k{[Y.sup.35 -(Y.sup.34 +Y.sup.36)/2].sup.2 +[Y.sup.36 -(Y.sup.35 +Y.sup.37)/2].sup.2 }                          (3)

Assuming that camshaft 25 is mounted in the cylinder head 2 and arrangedaccording to the angular position shown in FIG. 2, in other terms withthe lobes of cams 26 and 27 at diametrically opposite positions withrespect to the associated valves 3, 3^(I), it is also assumed, aspreviously mentioned, that the position of journal 37 is defined by thedeviation value Y³⁷ =Y³⁷ _(Smax), while initial values, comprised withinthe associated variability ranges, are attributed to the deviations ofthe other journals (Y³⁴,Y³⁵ and Y³⁶).

Subsequent processings in unit 16 include the calculation of the elasticenergy variation, according to the mathematical formula (3), as thevalues Y³⁴, Y³⁵ and Y³⁶ vary, and the identifying of the specific ternof values that make the E value minimum. These processings involve, forexample, the calculation of the partial derivatives of the formula (3)with respect to the deviations of each of the three journals, theincrement (or decrement) of the value of one of the three deviationsY³⁴, Y³⁵ or Y³⁶ on the basis of the comparison between the calculatedderivatives and the associated variability ranges, a subsequent furthercalculation of the derivatives, a subsequent new increment (ordecrement) of a deviation value, and the repetition of these steps forminimizing the E value.

The procedure ends when it is no longer possible to proceed, in otherterms, for example, when all the deviations have reached a value that isat the limits of their associated variability ranges, or when theelastic energy becomes null, or after a certain number of repetitions(for example 100), ensuring the required accuracy.

In this way there are determined the values of the deviations Y^(j) forthe single journals 34-37 that minimize the elastic energy, and amongthese the deviation value Y³⁴ correlated to the journal 34 that ispositioned between the cams 26 and 27 that, according to the specificangular position, have lobes oppositely arranged with respect to valves3-3^(I). Then, for each of the two cams 26 and 27 there is calculatedthe gap G²⁶ (and G²⁷) that, in the absence of adjustment shims 11 (and11^(I)), exists between the surface of the cam 26 (and 27), incorrespondence with its associated base circle, and the bottom of therecess 10 (and 10^(I)) of the bucket type tappet 9 (and 9^(I)) of theassociated valve 3 (and 3^(I)) as follows:

    G.sup.26 =A.sup.10 +Y.sup.34 -B.sup.26

where A¹⁰ is the distance of recess 10 from the first longitudinalreference axis (block 47), and B²⁶ is the distance of the surface of cam26, in correspondence with its base circle, from the second longitudinalreference axis (block 51). The thickness values S¹¹ of the adjustmentshims 11 (and 11^(I)) to be inserted in each of the two recesses 10 (and10^(I)) associated with cams 26 and 27 are obtained by subtracting fromthe calculated gap value G²⁶ (and G²⁷) the value of the nominalclearance G^(nom) that it is desired be maintained between theadjustment shims 11 (and 11^(I)) and the base circles of the cams 26 and27.

    S.sup.11 =G.sup.26 -G.sup.nom

The procedure described (with reference to blocks 54-59) is repeated(block 60) for the other three angular positions chosen by camshaft 25,and at each repetition there are calculated the distances and thethickness values of the shims intended to cooperate with one of theremaining pairs of cams in phase (28, 29, 30 31, 32 33), and, hence, thechecking procedure ends (block 61).

Therefore, the herein described method makes it possible to foresee howthe clearance among the main journals 24-37 and associated seats6-6^(III) will be distributed over each journal-seat pair and at eachangular position taken by camshaft 25.

This possibility is extremely important for correctly calculating theclearance between each cam of the camshaft 25 and its associated valve3-3^(VII), as this calculation takes into account the transversalpositioning of the main journals 34-37 in the seats of the cylinder head2.

As described at the beginning of the description, the known methods foradjusting the clearance between the cams of a camshaft and theassociated valves regard various procedures (for example, the insertionof shims between the end of each valve and the bucket type tappet, orthe selection of appropriately thick bucket type tappets). Needless tosay, this invention can also apply to similar methods, as in such casestoo it is necessary to correctly calculate the distance between the basecircles of the cams and the associated bucket type tappets (or otherelements intended to displace with the valves), for defining the shimsto be inserted (or, in any case, to be modified) appropriate forobtaining the required clearance values.

The method according to the invention has been described with specificreference to a timing system of an engine with four valves per cylinder.However, the method is particularly flexible and hence easily applicableto any timing system, regardless of the camshaft 25 configuration(number and axial and angular position of the cams on camshaft 25, etc.)and cylinder head 2 (number and axial and angular position of the valves3-3^(VII), etc.) undergoing the checking. Obviously, as the timingsystem configuration varies, there are changes, for example, in thenumber and the arrangement of the feelers, and/or the number of theangular positions taken by the camshaft in which dimensions are detectedand processed, but the processings that are performed do notsubstantially change.

Furthermore, the method herein described avoids using empiric and nottoo accurate procedures for calculating the thickness of the shims(11-11^(I)) to be inserted in recesses 10-10^(VII) of the bucket typetappets 9-9^(VII) of valves 3-3^(VII) and, consequently, it permits toreduce the number of out-of-tolerance parts and the processing time.

There can be foreseen variants with respect to what has been describedhereinbefore, without departing from the objects and the scope of theinvention.

For example, the detectings described with reference to the firstchecking station 1 can also be performed at two distinct checkingstations. A first checking station, including gauging heads with pairsof feelers, measures the inside diameter of the seats 6-6^(III) of thecylinder head 2, with the caps 5 still to be removed further to themachining of seats 6-6^(III) by a suitable machine tool, while a secondchecking station with gauging heads and feelers detects the arrangementof the recesses 10-10^(VII) of bucket type tappets 9-9^(VII), and thearrangement of the lower generating lines 17 of seats 6-6^(III)subsequently to the mounting of the cylinder head in the associatedcylinder block and the removal of caps 5. It is possible to immediatelydetermine, by processing in a simple way the diameter values and thevalues relating to the arrangement of the lower generating lines 17 ofthe seats 6-6^(III), the arrangement of the upper generating lines 44 ofthe seats. According to this embodiment of the invention, it is possibleto measure more easily the arrangement of the recesses 10-10^(VII) ofthe bucket type tappets 9-9^(VII) and keep into account, uponcalculating the shims 11, 11^(I), the deformations that the cylinderhead 2 undergoes when it is mounted in the cylinder block.

The checking stations can include checking means that differ from thosedescribed (in a very schematic way), and comprise, for example, opticaltype heads, or heads of another type.

The storing, processing and display unit 16 can be connected to eachchecking station, or not be directly connected to the checking stations.Under this second circumstance, the data detected by each checkingstation are stored in a magnetic support that accompanies each element(cylinder head 2 and camshaft 25) along all the production line andcontains the results of all the measurements taken. The data arethereafter entered--by means of a scanner--in the storing, processingand display unit 16, that performs the necessary processings.

In order to obtain the values of the deviations Y^(j) that bestapproximate the arrangement of camshaft 25 once it is mounted incylinder head 2, it is possible to follow a different principle withrespect to the one herein described, based on the checking of a numberof mechanical conditions in the coupling camshaft/cylinder head, butthat in any case allows to foresee, at every angular position taken bythe camshaft, the distribution of the clearance existing between themain journals 34-37 and the seats 6-6^(III) over every single journal34-37.

What is claimed is:
 1. Method for the dimension checking of the timingsystem of an internal combustion engine comprising at least a camshaft(25) with cams (26-33) and main journals (34-37), and a cylinder head(2) with valves (3-3^(VII)) and seats (6-6^(III)) for housing the mainjournals (34-37) and defining the position of said camshaft (25) in alongitudinal direction, the method including the steps ofdetecting andprocessing (50,51) values relating to diametral dimensions of the mainjournals (34-37) of the camshaft (25) and radial dimensions of the cams(26-33), detecting and processing (46,47) values relating to diametraldimensions of the seats (6-6^(III)) of the cylinder head (2), and thetransversal arrangement of the valves (3-3^(VII)) with respect to saidlongitudinal direction, and calculating (59)--on the basis of thedetected values and in the course of the camshaft (25) rotation--aclearance value (G²⁶) between each cam (26-33) and its associated valve(3-3^(VII)), characterized by the further steps ofcalculating (54-58),on the basis of said detected values, the deviation values (Y^(j)) thatrepresent the transversal position of each main journal (34-37) in itsassociated seat (6-6^(III)), and processing (59) the deviation values(Y^(j)) with said detected values for calculating said clearance value.2. The method according to claim 1, for checking a timing systemcomprising bucket type tappets (9-9^(VII)) associated with the valves(3-3^(VII)), wherein the step of detecting and processing valuesrelating to the transversal arrangement of the valves (3-3^(VII)) withrespect to said longitudinal direction comprises detectings (46)relating to the transversal arrangement of the bucket type tappets(9-9^(VII)), and the step of calculating, in the course of the rotationof camshaft (25), a clearance value between each cam (26-33) and itsassociated valve (3-3^(VII)), comprises calculating (59) the clearancevalue (G²⁶) between each cam and a surface of the associated bucket typetappet (9-9^(VII)).
 3. The method according to claim 1, wherein thesteps of detecting and processing values relating to the diametraldimensions of said main journals (34-37) and said seats (6-6^(III)),respectively, comprise processings (47,51) of said values for defining afirst and a second longitudinal reference axis, respectively, andreferring the detected values to these axes.
 4. The method according toclaim 3, wherein the step of calculating the deviation values comprisesprocessings (54) for defining, for each pair consisting of a mainjournal (34-37) and its associated seat (6-6^(III)), a range of values(Y^(j) _(Imax) -Y^(j) _(Smax)) within which said deviation is comprised.5. The method according to claim 4, wherein said step of calculatingsaid deviation values comprises the steps ofevaluating (56) the elasticenergy stored by said camshaft (25) at each of different angularpositions (53) taken by said camshaft (25), and calculating (56-58)--foreach of said different angular positions taken by camshaft (25)--thedeviation values (Y^(j)) that correspond to a minimum value of storedelastic energy.
 6. The method according to one of the preceding claims,wherein the steps of detecting and processing the values relating to thediametral dimensions of said main journals (34-37) and said seats(6-6^(III)), respectively, comprise the detecting of distances (46,50)relating to lower generating lines (40,17) and upper generating lines(41,44) of said journals and seats, respectively.
 7. Apparatus forchecking the timing system of an internal combustion engine according tothe method described in claim 1, comprising a first checking station (1)with a structure (13) for supporting and referring said cylinder head(2) and first detecting devices for providing signals responsive to thearrangement of the internal surfaces of the seats (6-6^(III)) and to thetransversal arrangement of the valves (3-3^(VII)), a second checkingstation (20) with support elements (22, 23) that define a longitudinalgeometrical axis for supporting the camshaft (25) in different angularpositions about said longitudinal geometrical axis and second detectingdevices for providing, for each of said different angular positionstaken by camshaft (25), signals responsive to the arrangement of thesurfaces of the main journals (34-37), and to the radial dimensions ofthe base circles of the cams (26-33), and a memorizing, processing anddisplay unit (16) for receiving and processing the signals of said firstand second detecting devices.
 8. A checking apparatus according to claim7, wherein said first detecting devices comprise first gauging heads(14) for providing signals responsive to the arrangement of the internalsurfaces of the seats (6-6^(III)) and second gauging heads (18) forproviding signals responsive to the transversal arrangement of thevalves (3-3^(VII)).
 9. An apparatus according to claim 8, for checking atiming system comprising bucket type tappets (9-9^(VII)), wherein saidsecond gauging heads (18) cooperate with surfaces of the bucket typetappets (9-9^(VII)) and provide signals responsive to the transversalarrangement of the bucket type tappets (9-9^(VII)).
 10. A checkingapparatus according to one of claims from 7 to 9, wherein said seconddetecting devices comprise third gauging heads (38) for providing, foreach of said different angular positions taken by camshaft (25), signalsresponsive to the arrangement of the surfaces of the main journals(34-37), and fourth gauging heads (42) for providing--for each of saiddifferent angular positions taken by camshaft (25)--signals responsiveto the radial dimensions of the base circles of the cams (26-33).
 11. Achecking apparatus according to claim 10, wherein said support elementsof the second checking station (20) comprise a live center (22) and adead center (23) that define said longitudinal geometrical axis.
 12. Anapparatus according to claim 11, wherein said second checking station(20) comprises a motor (24) coupled to said live center (22) for therotation of the camshaft (25) about said longitudinal geometrical axis.